High damping capacity due to two-step phase transformation in Ni–Ti, Ni–Ti–Cu, and Fe–Cr–Mn alloys

Abstract

In high damping materials, phase transformation is one of the most effective mechanisms. In this study, both Ni–Ti or Ni–Ti–Cu alloy and Fe–Cr–Mn alloy were investigated. Ni–Ti and Ni–Ti–Cu alloy were made by lamination and diffusion process and the phase transformation were B2→B19′ in the former and B2→B19→B19′ in the latter. The damping capacity was higher in B19 than in B19′, which were observed in two-step transformation. In Fe–Cr–Mn martensitic transformation was obtained through γ→α′ or γ→ε→α′ depending on composition and heat treatment. The maximum damping capacity was obtained in the ε phase, which was observed in a two-step transformation. For those cases, the d-electron concept was applied. Parameters B 0 and Md were used. B 0 represents the bond order which is related with bonding strength. Md represents the energy level of d-electron, which is related with electronegativity or atomic size of the elements. In the B 0 vs. Md map for Ni–Ti and Ni–Ti–Cu alloy the region for B19 formation was shown. In Fe–Cr–Mn the region for ε formation by cold work was also shown. Those areas corresponded to high damping regions. Therefore those maps would be effective for finding high damping region in each alloy.